Apart from synthetic materials from thermoplastic or thermosetting polymers, in many fields, for example in the automotive, packaging, furniture, electric and electronics industry as well as in the field of construction and the like, occasionally synthetic materials from thermoplastic or duroplastic polymers from polymers containing fiber structures or polymers containing fibers or fiber-reinforced polymers are used. Such materials are frequently produced as semifinished products, for example in the form of web materials, matting, boards etc. These are used immediately or only after further processing or refining and finishing, for example by molding, coating or the like. In addition to fiber materials, or instead of fiber materials, these polymeric materials may comprise suitable fillers to lend them specific properties. The variety and the number of options of applications of these bond materials comprising a great variety of polymers, fibers and fillers is almost unlimited.
Within the scope of increased environmental awareness and restrictive laws, the ability for recycling of materials or their environmentally harmless disposal plays an increasingly more important role. In particular, the ecologically compatible waste disposal assumes increasingly critical significance since the recyclability is limited due to growing contamination and material damages and in this case the elimination becomes unavoidable. This may be carried out by combustion or forming deposits. An unlimited formation of deposits may be made in public locations. The perpetual waste disposal unlimited in time is not possible for reasons of space. A particularly simple and advantageous form of elimination is the biological degradation which can occur, for example, through composting. If the expression "biologically degradable" herein-below is used, it is intended to be understood that the corresponding substance is accessible to degradation through living organisms (organisms/microorganisms) and/or through natural environmental factors, for example the chemical degradation through bacteria, fungi, in particular molds and yeasts. Synthetic materials which are commonly used in packaging materials, in particular polystyrene, are not biologically degradable. In the case of carbohydrates the biological degradation, for example primarily in the form of anaerobic bacterials decomposition, leads to harmless lower fatty acids, alcohol and carbon dioxide. This is referred to by the term "rot". Intermediate products of the rotting processes can combine to form harmless new polymeric products and this advantageous humification is utilized in composting. This process involves in particular the biological degradation or the conversion of organic substances, in particular organic wastes, wood, leaves, and other plant materials, paper and sewage sludge, which proceeds with the development of heat ("spontaneous heating") and leads to the formation of compost, a dark, crumbly substance with advantageous components of nutrient salts (phosphate, nitrogen and potassium compounds) (see Rompp Chemie-Lexikon, 9th Edition, Vol. 3, 1990, pp. 2312/2313).
In view of the mentioned possibilities of subjecting specific waste materials to biological degradation, natural products are increasingly therefore of interest in material development. They offer many advantages. As regenerated raw materials they contribute to the protection of resources. They are further largely nontoxic and can be combusted without leaving residues. Their degradation products are compatible with environmental protection.
Materials of wood chips or natural fibers, such as cellulose, cotton, bast fibers and wool have been processed for a long time into known products, such as paper, cardboard, felts, fiber boards and particle board. These wood chips or natural fibers can also serve for the manufacture of preforms (molded bodies) according to different processes. There is also a a great number of new developments in which high-strength natural fibers such as flax, hemp, ramie and the like, whose mechanical properties are to some extent comparable to those of synthetic high-performance fibers, are used as reinforcing fibers in bond or composite materials. The old and the new materials have in common the feature that they must comprise a synthetic polymer or synthetic polymers as bonding agents to achieve strength, stiffness, good molding properties or durability. However if biological degradability is required, only natural bonding agents such as starch, rubbers etc. can be considered. However, there is the disadvantage that they are soluble in water.
The development of replacing synthetic, biologically non-degradable polymers in the bond materials by biodegradable polymers has not yet been concluded. Natural products, such as cellulose, starch etc. as directly moldable substances are not suitable for most purposes or are inferior to synthetic polymers with respect to variability of properties and processing. Biodegradable novel polymers suitable for composites are, for example, the polyhydroxy butyrates, but these are very expensive.
In bond and composite materials the mixing ratio of bonding means components and reinforcement or filler components can fluctuate within wide limits. The portion of the polymer bonding means depends only on the properties required for the particular applications. For insulating materials or specific packaging materials, for example relatively soft web materials or specific packaging materials, for example soft web materials with low amounts of polymer bonding means are suitable. However also hard and stiff fiber boards can be produced with low mixtures of bonding means. On the other hand, for viscoplastic and waterproof materials and materials suitable for thermoforming, higher amounts of polymers are necessary. If in the final analysis the material properties are to be largely determined by the polymer, potentially only small additions--only for purposes of modification--of filler or reinforcement materials are necessary.
Moldable semifinished products, for example, for automobile parts, such as paneling, for example door paneling, roof ceiling and the like, are currently produced in large quantities with resin-bonded fiber matting comprising glass fibers, wood fibers, reprocessed cotton or bast fibers. Phenolic resins are predominantly used as the polymer. However, this is controversial from a toxicological and ecological point of view. Therefore, increasingly also other thermosetting materials, such as epoxides or unsaturated polyesters, are being used. Thermosetting bonding agents offer the advantage that they do not tend to become deformed at the temperatures in cars, which to some extent can be extreme. However, there are the drawbacks in the use of thermosetting bonding agents that the processing is complex and the price is high. In particular, epoxides, for example, are relatively expensive. A further drawback is that cured thermosetting materials can only be recycled with difficulty. For these reasons, other fiber-reinforced thermoplastic polymers, most often polypropylene, are currently used to a large extent. However, these polymers have low thermal dimensional stability. As an alternative to glass fibers natural fibers, such as cellulose are used or jute, but also wood powder. The materials for molded bodies known so far, comprise as a rule at least 20% by weight of polymers. Due to this relatively high amount of polymer the fibers are enveloped and bonded in such a manner that their biodegradability is no longer possible.
As insulating material for the thermal insulation of buildings there are used in large quantities glass fibers or mineral fiber matting which are bonded with low amounts of thermosetting materials, such as phenolic or urea resins. Due to toxicological considerations against the use of mineral fibers and their uncertain disposal, natural fiber matting is being increasingly developed and offered for sale. Depending on the production process, these fibers must also be strengthened with suitable polymer bonding agents. For example, for thermal strengthening, readily melting, synthetic bonding fibers are being used. However, these fibers conflict with the demand for biological degradability.
Various publications, for example "Verpackung aus nachwachsenden Rohstoffen (Packaging of regenerated raw materials"), Vogel Buchverlag, Wurzburg, 1st Edition, 1994, pp 146-148 as well as 374-380, "Nachwachsende und biobbaubare Materialien im Verpackungsbereich (Regenerated and biodegradable materials in the packaging field"), Roman Kovar Verlag, Munchen, 1st Edition, 1993, pp. 120-126 as well as 463 and DE 39 14 022 A1, describe a raw material which is readily biologically degradable by composting and which is based on cellulose acetate and citric acid esters and its use for the production, for example of wrappings or containers for oil lights, eternal oil candles, composition oil lights, other light implementations for graves and foils. In addition to the specified materials, this synthetic material comprises polyesters and if necessary other organic acids and/or acid esters. The citric ester serves as softener and results in the capability of the cellulose acetate to be processed thermoplastically so that it can be formed into a molded body.
The article "AVK-Tagung Faserverstarkete Kunststoffe Weg zuruck zur Natur" (AVK Conference Fiber Reinforced Synthetic Materials--the path back to nature), by Wolfgang Asche in the Journal "Chemische Rundschau", No. 39, 30 September 1994, p. 3, describes the use of the above mentioned synthetic material, described inter alia in the cited publication "Verpackung aus nachwachsenden Rohstoffen", based on cellulose diacetate and citric acid esters together with natural fibers, such as ramie, flax, sisal or hemp, for the production of composite materials. The described moldable material based on cellulose diacetate, citric acid esters and polyesters and if necessary other organic acids and/or acid esters as well as natural fibers, ramie, flax, sisal or hemp can be processed into molded bodies which can be readily degraded biologically. Because of the high prices of the synthetic material, they are relatively expensive. A drawback in particular is the portion of citric acid ester as softener. During the processing of these materials this softener can escape at high temperatures which can lead to undesirable vapors or smoke loads. The softener can also migrate at normal temperatures to the surface of the material and can evaporate impairing the environment. Due to the incorporation of the low-molecular softener the finished product also experiences a loss of strength. It has further a rather low softening point, which is due to the softener.
United States Patent; U.S. Pat. No. 3 271 231 relates to a flexible fiber web free of support comprising cellulose acetate fibers and cellulose fibers. By necessity, in its production a softener is used in the amount of 2 to 8% by weight. This patent shows that the cellulose acetate is not completely plastified but rather is only softened and bonds the cellulose fibers at their points of contact. In this manner flexible molded sheet objects with an open structure are obtained.
The known processes for the production of molded bodies based on cellulose acetate and reinforcing natural cellulose fibers as well as the molded bodies produced accordingly require absolutely the presence of softeners. However, this is a drawback from a number of points of view. The softener leads, for example, to a lower thermal stability under load, as a measure of which, for example, the Vicat temperature can be used. The thermal stability under load of the known materials is insufficient for applications, for example, in the automobile industry, where markedly higher Vicat temperatures are desired. On the other hand, the use of softeners in the thermal molding of cellulose acetate has been considered among experts to be absolutely necessary. Pure cellulose acetates can hardly be melted without degradation since their softening is always accompanied by thermal degradation. For example, the monograph "Cellulose and Cellulose Derivatives", Vol. V, Part 3, Emil Ott, H. M. Spurlin explains on page 1364: ". . . softening and degradation of 2.5 cellulose acetate is in the range of 235.degree. C. to 270.degree. C. . . . ". One skilled in the art must thus assume that during the thermal shaping of cellulose acetates, softeners are always required.